I'm looking for something I can put behind ink-jet printed pictures to keep them from bending, but I don't want to increase the thickness of the final product any more than necessary.
The thinnest balsa wood works but is expensive in 8" wide sheets. Manila folder material sort of works but I would prefer that it was more rigid than that.
80lb. card stock adds too much thickness.
I am not adverse to reusing salvaged materials for this.